(18) Tidal forceJan 25, 2013

The tidal force causes tides and is inversely proportional to the cubic of the distance between two celestial bodies. Since the moon is close to the Earth, the tidal force of the moon is 2.2 times as strong as that of the Sun. The position of the moon determines when high and low tides occur. A spring tide occurs when the moon is full or new, while a neap tide occurs when the moon is in its first and third quarters. In addition, the tidal force at perigee becomes further strong because of the moon's elliptical orbit. Do you know that the tidal force slows the Earth's rotation at 17 microseconds per year and causes the moon to recede from the Earth at 3.8 cm per year? How did the Earth look like several billion years ago then? You can imagine that the Earth was closer to the moon and was rotating faster and that the sea water was so choppy that it was having a big influence on the evolution of the life.
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